Many types of T-attachments are used in dentistry in order to fasten prostheses and removable bridges. Such devices are illustrated for example in U.S. Pat. No. 4,196,516 and European Patent Specification No. 0,085,781. They consist of a male part of patrix and a female part or matrix. The matrix surrounds the patrix to a large extent, in order to assure a firm seating of the patrix in the matrix. Usually, the patrix is slotted from the occlusal or the gingival side. The lamellae formed by the slot are bent up by widening the slot with special tools. This feature imparts an additional friction to the patrix so that the patrix is seated even more firmly in the matrix. This process is designated as "activation".
The coupling area between the residual teeth and the removable prosthesis is an area which is particularly heavily stressed in the mouth. Especially during movements about the transverse axis, the slot in the patrix is gradually compressed, regardless of whether the slot is located in the occlusal or the gingival area of the patrix. Since this causes the seating of the patrix in the matrix to become loose, these T-attachments must be reactivated at frequent intervals to assure that the prosthesis is firmly seated in the mouth.
T-attachments are also used in which the patrix is provided with a continuous slot and the patrix halves are held together by a partially slotted longitudinal beam of the patrix. The slot is spread by means of a screw provided with a conical head. This screw is turned sagittally into the front surface of the slotted patrix. However, the spread-apart patrix body is rigid after activation, since the elastic patrix halves are supported on the screw head. In addition, the patrix parts are mechanically weakened by the position of the screw on the front surface of the patrix. The correct point of friction is difficult to find in rigidly fixed parts, so that, in the case of an over-activation, the patrix can easily be jammed in the matrix. In case there is insufficient activation, the friction is insufficient.